Diffusers are used in order to condition the compressed fluid (usually air) of a gas-turbine engine before it is fed to the combustor, where it is mixed with fuel, the resultant mixture being used to drive the turbine.
A typical gas-turbine engine with a diffuser is shown in FIG. 1 in simplified form. This diagram is taken from U.S. Pat. No. 6,513,330, issued on 4 Feb. 2003 and assigned to the Allison Advanced Development Company.
The engine shown as reference numeral 10 in FIG. 1 is a turbo-fan engine for an aircraft and comprises a fan section 12, a compressor section 14, a combustor section 16 and a turbine section 18. The compressor section 14 includes a rotor 20, which has coupled to it a series of compressor blades 22. The rotor 20 is secured to a shaft 24, which rotates within the engine. A plurality of compressor vanes 26 are disposed next to the blades 22 and serve to direct the flow of gaseous fluid through the compressor section. At the downstream end of the compressor section is a number of compressor outlet vanes 26′ for directing the flow of fluid into an annular diffuser 28. As mentioned above, the diffuser conditions the fluid and discharges it into the combustor section for subsequent combustion.
Typically, a diffuser may be made in two halves, which fit together to form a ring. Thus the two halves are arcs of a circle. When the diffuser is fitted, the lower half is attached to the lower part of the engine, then the rotor is fitted, then the upper half of the diffuser is offered up to the lower half over the rotor, finally the upper part of the engine is offered up to the lower part of the engine and secured thereto in a manner which also clamps the two diffuser halves together. While this sounds like a relatively simple process, in practice it is complicated by the difficulty experienced in keeping the two halves of the diffuser in proper alignment with each other while the rotor is being fitted and the upper part of the engine is attached. Any relative movement between the two halves of the diffuser at this time may result in the diffuser halves being permanently misaligned, with consequent reduction in diffuser performance.